<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    p {
        color: blue;
    }
    .container p {
        color: red;
    }
    #main p {
        color: green;
    }
</style>
<body>
    <div id="main" class="container">
        <p>这是一个段落</p>
    </div>
</body>
</html>